LOCATION DOWNSOUTH ILEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Mollic Oxyaquic Hapludalfs
TYPICAL PEDON: Downsouth silt loam, with a northwest-facing slope with a 3 percent gradient on a convex summit in a cultivated field at an elevation of about 560 feet above sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 9 inches; very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; moderate fine granular structure; friable; many very fine roots; few fine and medium continuous tubular pores; about 20 percent clay; neutral; abrupt smooth boundary. (7 to 9 inches thick)
E--9 to 13 inches; brown (10YR 4/3) silt loam, pale brown (10YR 6/3) dry; moderate thick platy structure parting to moderate medium granular; friable; common very fine roots; common fine and medium continuous tubular pores; few distinct light gray (10YR 7/2) dry clay depletions and common distinct very dark grayish brown (10YR 3/2) organic coatings on faces of peds; about 22 percent clay; slightly acid; clear smooth boundary. (0 to 6 inches thick)
Bt1--13 to 26 inches; dark yellowish brown (10YR 4/4) silty clay loam; moderate fine prismatic structure parting to strong fine subangular blocky; firm; common very fine roots; common fine and medium constricted tubular pores; few distinct light gray (10YR 7/2) dry clay depletions and many distinct dark brown (10YR 3/3) clay films on faces of peds; few fine rounded strong brown (7.5YR 5/6) masses of iron-manganese accumulation; about 32 percent clay; moderately acid; clear smooth boundary.
Bt2--26 to 38 inches; yellowish brown (10YR 5/4) silty clay loam; moderate medium prismatic structure parting to moderate fine and medium subangular blocky; firm; common very fine roots; few very fine and fine constricted tubular pores; many distinct dark brown (10YR 3/3) clay films on faces of peds; few fine distinct light brownish gray (10YR 6/2) iron depletions and common fine distinct yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine irregular very dark brown (7.5YR 2.5/2) masses of iron-manganese accumulation with clear strong brown (7.5YR 5/6) boundaries; about 30 percent clay; slightly acid; gradual smooth boundary.
Bt3--38 to 57 inches; brown (10YR 5/3) silty clay loam; weak medium prismatic structure parting to weak medium subangular blocky; firm; few very fine roots; few very fine and fine constricted tubular pores; common distinct brown (10YR 4/3) clay films on faces of peds; common fine faint light brownish gray (10YR 6/2) iron depletions and many fine and medium distinct yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine and medium irregular very dark brown (7.5YR 2.5/2) masses of iron-manganese accumulation with clear strong brown (7.5YR 5/6) boundaries; about 28 percent clay; slightly acid; gradual smooth boundary. (Combined thickness of the Bt horizons is 36 to 48 inches.)
BCt--57 to 65 inches; brown (10YR 5/3) silt loam; weak medium and coarse subangular blocky structure; friable; few very fine roots; few very fine and fine tubular and vesicular pores; few distinct brown (10YR 4/3) clay films on faces of peds and lining root channels and pores; many fine and medium faint light brownish gray (10YR 6/2) iron depletions and common fine and medium distinct yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine and medium irregular very dark brown (7.5YR 2.5/2) masses of iron-manganese accumulation with clear strong brown (7.5YR 5/6) boundaries; about 26 percent clay; neutral; gradual smooth boundary. (0 to 12 inches thick)
CB--65 to 80 inches; pale brown (10YR 6/3) silt loam; massive; friable; few very fine roots; many very fine to medium tubular and vesicular pores; few distinct brown (10YR 4/3) clay films lining small root channels and pores and very few prominent very dark grayish brown (10YR 3/2) organo-clay coatings filling large root channels and pores; common fine and medium faint light brownish gray (10YR 6/2) iron depletions and many fine and medium distinct yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few fine and medium irregular black (7.5YR 2.5/1) masses of iron-manganese accumulation with clear strong brown (7.5YR 4/6) boundaries; about 20 percent clay; neutral.
TYPE LOCATION: St. Clair County, Illinois; about 1 mile south of Belleville along State Route 15; approximately 600 feet south and 550 feet east of the northwest corner of sec. 19, T. 1 N., R. 8 W.; USGS FRENCH VILLAGE, IL. topographic quadrangle; lat. 38 degrees 31 minutes 30 seconds N. and long. 90 degrees 02 minutes 04 seconds W. NAD 27.
RANGE IN CHARACTERISTICS: Depth to the base of the argillic horizon is 42 to 70 inches. Depth to carbonates, where present, is greater than about 5 feet. The particle-size control section averages 27 to 35 percent clay. Sand content is less than 7 percent in all parts.
The Ap horizon has value of 3 (5 dry) and chroma of 2 or 3. In undisturbed areas the A horizon has value of 2 or 3 (4 or 5 dry) and chroma of 1 or 2. Clay content is 18 to 27 percent. Reaction is moderately acid to neutral, depending on the liming history.
The E horizon, where present, has value of 4 or 5 and chroma of 2 or 3. When the soil is dry, common gray to white clay depletions are easily discernible on faces of peds in the E and B horizons, but these features are not readily apparent when the soil is moist. Clay content is 18 to 27 percent. Reaction is strongly acid to neutral.
Some pedons have an EB or a BE horizon.
The Bt and BC horizons have hue of 7.5YR, 10YR, 2.5Y; value of 4 to 6; and chroma of 3 to 6 (2 to 6 in the lower part). Redoximorphic iron depletions are in the lower part, above 40 inches. Texture typically is silty clay loam, but the lower part includes silt loam. Clay content is 27 to 35 percent in the upper part and is 24 to 32 percent in the lower part. Reaction is strongly acid to neutral.
The CB or C horizon has hue of 7.5YR, 10YR, or 2.5Y; value of 5 or 6; and chroma of 1 to 4. Clay content is 18 to 27 percent. Reaction is moderately acid to slightly alkaline.
COMPETING SERIES: These are the
Barony,
Grays,
Hedrick,
Kaneville,
Newvienna,
Richview,
Throckmorton,
Windere, and
Wingate series.
Barony, Grays, Kaneville, Richview, Throckmorton, Windere, and Wingate soils contain more than 7 percent sand in the lower part of the series control section. Hedrick and Newvienna soils have a mean annual soil temperature less than 56 degrees F.
GEOGRAPHIC SETTING: The Downsouth soils are on gently sloping to moderately sloping convex summits, shoulders, and backslopes. Slope ranges from 2 to 10 percent. These soils formed in loess. Mean annual temperature is 54 to 57 degrees F., mean annual soil temperature is 56 to 59 degrees F., mean annual precipitation is 36 to 40 inches, frost-free period is 170 to 200 days, and elevation is 400 to 800 feet above sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bethalto, Wakenda, and Winfield soils. The somewhat poorly drained Bethalto soils form a hydrosequence with the Downsouth soils. They are on less sloping summits nearby. The well drained Wakenda soils have a mollic epipedon. The moderately well drained Winfield soils are on similar landform positions closer to the drainageways.
DRAINAGE AND PERMEABILITY: Moderately well drained and moderate permeability. The potential for surface water runoff is medium. Depth to an intermittent apparent high water table is 2.0 to 3.5 feet from January to April in most years.
USE AND VEGETATION: Most areas are cropped to corn, soybeans, and wheat. A few areas are pastured or wooded. Native vegetation is mixed prairie grasses and deciduous trees.
DISTRIBUTION AND EXTENT: Southwestern Illinois. Extent is moderate, and mainly in MLRA 115.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: St. Clair County, Illinois, 1997. The Downsouth series was named for the southern extent of the Downs series.
REMARKS: Downsouth soils were formerly included with the Downs series (Mollic Hapludalfs) or the inactive Sicily series.
Diagnostic horizons and features recognized in this pedon are: Ochric epipedon - the zone from the surface to a depth of 13 inches (Ap and E horizons). Argillic horizon - the zone from approximately 13 to 57 inches (Bt1, Bt2, and Bt3 horizons). Redoximorphic iron depletions - the zone from 26 to 80 inches (Bt2, Bt3, BCt, and CB horizons). Udic moisture regime.